A sunlight power generation using a solar cell is environmentally-friendly and has merits over a power generation using fossil fuel, such that air pollution or noise does not occur and an energy source, i.e. sunlight, is not depleted. Among various solar cells, a dye sensitized solar cell based on nanocrystalline porous titanium oxide (TiO2) has been highlighted and studied extensively due to high energy conversion efficiency and a low manufacturing cost.
The dye sensitized solar cell which may be a third-generation solar cell has also been highlighted particularly in its low manufacturing cost which may be about one-fifth of that of the silicon solar cell in addition to high energy conversion efficiency. Further, since a transparent conductive glass substrate is used and modules having various colors may be manufactured with various dyes and electrolytes, the dye sensitized solar cell may be applied to a window of a building and the like.
The dye sensitized solar cell may be constituted with a photoelectrode including an oxide semiconductor electrode adsorbed with a dye on a surface thereof on a conductive substrate, an electrolyte capable of oxidizing and reducing reaction, and a counter electrode where a catalyst electrode is formed on a conductive substrate. When light is radiated on the dye sensitized solar cell, the dye absorbs energy of the light to generate an electron-hole pair, and the generated electron is injected into a conduction band of an oxide semiconductor. The injected electron is subsequently transported through the oxide semiconductor to a transparent electrode, and moves through an external circuit when the photoelectrode and the counter electrode are connected, thereby generating an electric current. The electron-hole generated in the dye receives electrons from the electrolyte which is capable of oxidizing and reducing and is reduced back, thereby restoring the dye sensitized solar cell and completing an electric circuit of the dye sensitized solar cell. In this case, the counter electrode may provide the electron moving through the external circuit, thereby triggering an oxidation-reduction reaction of ions in the electrolyte. Since the electron to the electrolyte needs to be efficiently transferred, the counter electrode typically has a structure where the conductive substrate is coated with the catalyst. In addition, the catalyst may require substantial level of catalytic activity, increased surface area and elevated electrical or ion conductivity to thereby have a minimal electrical resistance at interface with the electrolyte and further require long-term stability in the electrolyte. Moreover, the electrolyte used in the dye sensitized solar cell may have an elevated boiling point to simultaneously obtain substantial durability and improved ionic conductivity affecting efficiency.
In the related arts, compositions used as the electrolyte of the dye sensitized solar cell have been described as follows.
For example, an electrolyte for a dye sensitized solar cell has been reported and the electrolyte includes an imidazole-based oligomer type ionic liquid N-(3-(1-methylimidazolium)propyl)hexanamide iodide (NMIPHI), the imidazole-based oligomer type ionic liquid has N-alkylimidazolium propylhexanamide iodide as a basic structure and includes an iodine ion (I−) that is an inorganic anion. The electrolyte may be present in a solid or liquid state according to substitution of a reaction group of an organic cation, and the electrolyte is manufactured by adding iodine, 4-tert-butylpyridine (TBP), and 3-methoxypropionitrile (MPN) to the ionic liquid (e. g. Korean Patent Application Laid-Open No. 2013-0084719).
Also provided in the related arts is an electrolyte for a solar cell, which includes a complex salt of imidazole and C1-C20 diiodoalkane, and a cation of a complex of imidazole and C1-C20 diiodoalkane and iodine ions (I−/I3−) generated from iodine (I2), and a solar cell using the electrolyte has also been developed. The electrolyte further includes 1 to 10 parts by weight of a nonvolatile organic solvent such as acetonitrile, gamma-butyrolactone, and 3-methoxypropionitrile in addition to the aforementioned electrolyte (e.g. Korean Patent Application Laid-Open No. 2009-0022383).
In other example in the related art, an imidazole-based polymer type or oligomer type ion solution has been developed. The ion solution includes an iodine ion (I−) and 1 to 25 ethylene oxide monomers and has a structure of the ethylene oxide monomers and urethane in which urea is connected to the ethylene oxide monomers and an imidazolium structure at an end thereof. The electrolyte for a dye sensitized solar cell, which includes an organic solvent selected from acetonitrile, 3-methoxypropionitrile, gamma-butyrolactone, ethylene glycol, and the like in addition to the aforementioned ion solution has also been disclosed (e.g. Korean Patent Application Laid-Open No. 2011-0011158).
In addition, a dye sensitized solar cell including an imidazolium-based liquid type electrolyte has been reported. The imidazolium-based liquid type electrolyte may be in a liquid state at room temperature and elevated temperatures and having excellent thermal stability and temperature stability without using an organic solvent in an electrolyte. Thus, the dye sensitized solar cell including a semiconductor electrode; a counter electrode; and a 1,3-vinylalkylimidazolium iodide-based electrolyte interposed between the semiconductor electrode and the counter electrode has been provided (e.g. US Patent Publication No. 2004-0261842).
In another example of the related arts, an electrolyte solution for a dye sensitized solar cell has been developed. The electrolyte includes an organic solvent; an oxidation-reduction derivative; a pyrrolidinium iodide-based ionic liquid selected from the group consisting of 1-butyl-1-methylpyrrolidinium iodide, 1-methyl-1-propylpyrrolidinium iodide (MPPyI) and 1-ethyl-1-methylpyrrolidinium iodide; and t-butylpyridine as an additive, in which the organic solvent is one kind or more mixture solutions selected from ethylene carbonate, 3-methoxypropionitrile, gamma-butyrolactone, diethyl carbonate, and the like (e.g. Korean Patent No. 10-1088676).
Meanwhile, a polymer particle dispersing element, an electrolyte, and a cell have been provided and the electrolyte includes a polymer particle dispersing element containing polymer particles and an ionic liquid in which the polymer particles are monomer components and include methyl (metha)acrylate, isobutyl (metha)acrylate, cyclohexyl (metha)acrylate, and the like, and the ionic liquid includes 1-ethyl-3-vinylimidazolium or 1-methyl-3-ethylimidazolium iodide (e.g. Japanese Patent Application Laid-Open No. 2004-256711).
In some other related documents in the related arts, an electrolyte for a dye sensitized solar cell has been proposed. The electrolyte includes the imidazole-based oligomer type ionic liquid N-(3-(1-methylimidazolium)propyl)hexanamide iodide (NMIPHI) and a 3-methoxypropionitrile solvent. In addition, the solar cell includes the electrolyte including the complex salt of imidazole and C1-C20 diiodoalkane, and a cation of the complex salt and iodine ions (I−/I3−) generated from iodine (I2), and further includes the nonvolatile solvent such as acetonitrile. Moreover, the electrolyte for the solar cell has been proposed to include the imidazole-based polymer type or oligomer type ion solution including the iodine ion (I−) and 1 to 25 ethylene oxide monomers, and the organic solvent such as acetonitrile, and to include the imidazole-based compound and solvent. However, the electrolyte in such dye sensitized solar cell does not include the imidazolium-based compound such as 1-propyl-3-methylimidazolium iodide or the pyridinium-based compound as the ionic liquid, and thus stability may be significantly reduced (e.g. Korean Patent Application Laid-Open No. 2013-0084719; Korean Patent Application Laid-Open No. 2009-0022383; Korean Patent Application Laid-Open No. 2011-0011158).
Moreover, in other related documents, the dye sensitized solar cell including the 1,3-vinylalkylimidazolium iodide-based electrolyte has been disclosed. The electrolyte solution for the dye sensitized solar cell includes the organic solvent; the oxidation-reduction derivative; the pyrrolidinium iodide-based ionic liquid; and the additive. Further, the electrolyte includes the polymer particle dispersing element containing the polymer particles and the ionic liquid, but does not include the ionic liquid and the low viscosity liquid solvent, and thus performance may deteriorate. (e.g. US Patent Publication No. 2004-0261842; Korean Patent No. 10-1088676; Japanese Patent Application Laid-Open No. 2004-256711).
The above described conventional technologies in the related arts have been focused on preventing liquid leakage or volatilization of the electrolyte for the solar cell by simply using a general ionic liquid and maintaining stability thereof. However, particular solution has not been provided for an optimum composition of the electrolyte using the low viscosity solvent as the additive in the ionic liquid electrolyte, an efficiency improvement effect, and maintenance of endurance stability.
In particular, in order to apply a dye sensitized solar cell to vehicles, long term stability in an actual vehicle environment in a temperature range of about −40 to 85° C. may be required by using a high durability material which stably maintains performance even in a severe outdoor environment.
However, in the current technologies in the related arts using low boiling point liquid electrolyte, although efficiency may be improved, temperature durability may be inferior in the actual vehicle environment due to a low boiling point and flowability, and thus such liquid electrolyte may not be used for a vehicle. Meanwhile, when the electrolyte has improved durability and a viscosity greater than that of a liquid solvent, ion mobility may be reduced, and thus that solar energy conversion efficiency may be reduced low as compared to the liquid electrolyte.
Accordingly, in order to develop a dye sensitized solar cell for a vehicle, a novel electrolyte which satisfies both durability in a severe vehicle evaluation condition and improved efficiency is desired.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.